The Avengers also boasts impressive production values and special effects so good that every outrageous minute looks thrillingly convincing. You will believe a man can fly…and harness lightning in a hammer…and become a green rage monster…and survive a forest-leveling death blow from a mythological god.

The screenplay by director Joss Whedon (from a story by Zak Penn and Whedon) does a remarkable job of giving each hero enough to do that none of their fans will feel shortchanged. Downey’s Iron Man, aka inventor/egomaniac /smartass Tony Stark, rightfully gets the snappiest dialog. Frequently attired in a Black Sabbath T-shirt (“Iron Man,” get it?), he refers to the horn-helmeted Loki as “Reindeer Games” and describes himself as a “genius billionaire playboy philanthropist.” Gwyneth Paltrow reprises her role from the Iron Man movies as his playfully sexy assistant/love interest Pepper Potts.

Ruffalo succeeds Eric Bana (2003’s Hulk) and Edward Norton (2008’s The Incredible Hulk) as scientist Bruce Banner, who can transform into the massive and nearly mindless Hulk. Ruffalo’s Banner has an easygoing rumpled-professor charm, and his computer-generated alter ego fits seamlessly into scenes of citywide destruction. The Hulk also does something so funny that audiences may have trouble hearing the only two words he speaks in the movie over the audience’s laughter (but a Google search should reveal all).

Captain America, a duty-bound super-soldier suspended in ice for nearly 70 years after World War II, is endearingly “greatest generation” traditional. Advised that he may want to sit out a fight with the god Loki, Cap unironically replies, “There’s only one God, ma’am, and I’m pretty sure he doesn’t dress like that.” Hemsworth is the buffest of the bunch as the Shakespearean-sounding thunder god Thor, who gets to deliver stately lines like “a throne would suit you ill.”

Renner’s Hawkeye is the archer with an arrow for every occasion, brainwashed by Loki to betray his comrades. Johansson’s Black Widow is a coolly sexy one-time assassin who wants to repent for the “red in my ledger.”

The movie’s tone and characterizations owe a lot to comic book writer Mark Millar’s terrific 21st-century reboot of writer Stan Lee and artist Jack Kirby’s original Avengers concept. Also of interest to fans: a short teaser during the end credits features a villain that Marvel maniacs, but probably no one else, will recognize.

Minor complaints: Some nighttime and shadowy scenes look a tad too dark in the 3D version. The Avengers could have spent a little less time bickering and strategizing aboard the S.H.I.E.L.D. Helicarrier (basically an aircraft carrier that flies). And although Whedon mostly refrains from putting self-consciously ironic Buffy the Vampire Slayer-style dialog in anyone’s mouth but Tony Stark’s, where it fits, he gives Thor a quick gag about Loki that’s funny but entirely out of character.

Aside from trivialities like those, this entertainingly epic two-hours-plus blockbuster actually manages to be more than the sum of its superheroic parts. Also, spectacular scenes such as a big-finish battle royale in the heart of Manhattan make it worth seeing on the biggest screen possible.

Not only a great superhero movie, this is one of the best movies of the year.